1. Field of the Invention
The present invention relates to a vehicle occupant protection device which protects an occupant by using an airbag provided on a seat belt upon a vehicle collision.
2. Description of Related Art
FIG. 1 of Japanese Patent Application Publication No. 2006-044614 (JP 2006-044614 A) illustrates a occupant protection device which includes an upper airbag which is accommodated in a shoulder belt and to be inflated and expanded in the vicinity of a occupant's head and a lower airbag which is accommodated in a lap belt and to be inflated and expanded between the upper airbag and occupant's thighs. The upper and lower airbags are separate from each other and upon a front collision of a vehicle, are supplied with gas individually from an inflator so that they are inflated and expanded at the same time. In this occupant protection device, a occupant's head is restrained earlier by the upper airbag which is inflated and expanded from the shoulder belt upon the front collision.
Further, FIG. 5 of the JP 2006-044614 A illustrates a occupant protection device provided with the airbag which is accommodated in the shoulder belt and to be inflated and expanded between the head and the thighs. This airbag is formed by partitioning a single bag to an upper airbag and a lower airbag with a partition wall and gas from an inflator is supplied to the upper airbag. When the internal pressure of the upper airbag is increased as a result, gas flows into the lower airbag via a one-way valve provided on the partition wall. In this occupant protection device also, the occupant's head is restrained earlier by the upper airbag of the airbag which is inflated and expanded from the shoulder belt at the time of a front collision.
By the way, after the upper half of the occupant's body which is about to be inclined forward by the inertia force at the time of the front collision of the vehicle is retrained by the lower airbag and the shoulder belt as described above, the occupant's head is inclined forward relative to the chest and the like. If the forward inclining timing of the head and the inflation/expansion timing of the upper airbag described above deviate from each other largely, it can be considered that the upper airbag may interfere with the head carelessly.